Spinnerets for making cut-resistant yarns

ABSTRACT

The invention provides spinnerets for making yarns made of filaments of different average diameters.

FIELD OF THE INVENTION

The present invention relates to the field of spinnerets for spinning ofsynthetic fibres, in particular for making continuous filament yarnshaving mixtures of filaments of different deniers.

BACKGROUND OF THE INVENTION

Cut-resistant yarns are used for making fabrics which resist abrasion,cutting, tearing, penetration and puncture. Such fabrics can be used tomanufacture protective garments for workers in various industriesworking with abrasive materials or sharp objects, as well as for policeand military personnel requiring protection against stabbing implementsand projectiles.

Cut-resistant yarns can be made from glass, mineral fibres, steel, butincreasingly, synthetic polymer fibres are being employed, because theyprovide excellent cut-resistance, while offering a weight advantage, anda look and feel in the finished fabric that is similar if not identicalto regular fabric. Polymers that are used for cut-resistant yarnsinclude, for example, polyamides (e.g., p- and m-aramids), polyolefins(e.g., polyethylene), and polyazoles (e.g., PBO), and PIPD(poly-diimidazol pyridinylene dihydroxy phenylene, “PB”).

Yarns made from synthetic polymer fibres are made using various spinningprocesses, all of which involve the use of a spinneret having multiplesmall openings, through which a concentrated solution or suspension ofthe polymer (or molten polymer) is sprayed or extruded. After extrusion,the polymer solidifies (and consolidates) into filaments, which are thenspun into a multifilament yarn.

Examples of such spinning processes are described in the prior art. U.S.Pat. No. 4,078,034 discloses a method called “air gap spinning” in whicha solution of an aromatic polyamide is extruded from a spinneret into anair gap (approximately 9 mm) before passing into a coagulating bath. Inthe case of poly(p-phenylene terephthalamide) (p-aramid), the solutionconsists of 15-25% by weight p-aramid in concentrated H₂SO₄, and thecoagulating solution contains <20 wt % aqueous H₂SO₄, at a temperaturewhich is adjusted to below 35° C. for this quenching step.

In a process used for spinning m-aramid, a concentrated solution ofm-aramid in an amide solvent, such as N,N-dimethylacetamide (DMA) isextruded from a spinneret into an aqueous coagulation bath. Such aprocess is disclosed in U.S. Pat. No. 4,073,837.

The holes in the spinneret head are chosen to produce filaments of thedesired number and diameter. Filaments can be extended in air or gasbefore solidification (often referred to as “spin-stretch”), and/or in aliquid during the quenching/solidification process, and in many productsby drawing after the filaments have been initially quenched orsolidified. Drawing the filaments will reduce the average diameter.Multiple filaments are spun together to produce a yarn having a finallinear density that is a sum of the linear density of each of thefilaments.

Although existing synthetic yarns made with conventional spinningprocesses have excellent cut- and most of the time moderateabrasion-resistance, a need remains for yarns with excellent cut- andimproved abrasion-resistance.

SUMMARY OF THE INVENTION

The inventors have found that if filaments having different deniers arespun together into a single yarn, the resulting yarn has excellent cut-and abrasion-resistance.

In a first aspect, the invention provides a yarn, comprising:

a first plurality of continuous filaments, each of the first pluralityof filaments having an average diameter in the range of at or about 2 to25 (preferably 4 to 10) microns/filament;

-   -   at least a second plurality of continuous filaments, each of the        second plurality of filaments having an average diameter greater        than the average diameter of the first plurality of filaments,        and in the range of at or about 10 to 40 (preferably 10 to 32)        microns/filament; and    -   the first and second plurality of filaments being made of the        same polymer selected from the group consisting of an aromatic        polyamide, a polyolefin (preferably having a molecular weight        above at or about 1 million Da, such as an UHMWPE), PB, and an        aromatic polyazole.

In a second aspect, the invention provides a yarn, comprising:

-   -   a first filament, having an average diameter in the range of at        or about 4 to 25 microns;    -   a second filament, having an average diameter greater than the        average diameter of the first filament, and in the range of at        or about 15 to 40 microns/filament; and    -   a plurality of filaments having average diameters distributed        between the average diameter of the first filament and the        average diameter of the second filament;        wherein all of the filaments are made of the same polymer        selected from the group consisting of an aromatic polyamide, a        polyolefin (preferably having a molecular weight above at or        about 1 million Da, such as an UHMWPE), PB, and an aromatic        polyazole.

In a third aspect, the invention provides a yarn, comprising:

-   -   a first plurality of continuous filaments, each of the first        plurality of filaments having a first nominal linear density in        the range of 0.25 to 1.25 denier/filament;    -   at least a second plurality of continuous filaments, each of the        second plurality of filaments having a second nominal linear        density greater than the first nominal linear density and in the        range of 1.25 to 6 denier/filament; and    -   the first and second plurality of filaments being made of the        same polymer selected from the group consisting of an aromatic        polyamide, a polyolefin (preferably having a molecular weight of        at least 1 million Da), PB, and an aromatic polyazole.

In a fourth aspect, the invention provides a cut-resistant fabriccomprising the yarn of the invention.

In a fifth aspect, the invention provides a cut-resistant garment madeusing the cut-resistant fabric of the invention.

In a sixth aspect, the invention provides a method for making acut-resistant yarn, comprising the step of:

-   -   extruding a polymer selected from an aromatic polyamide, a        polyolefin (preferably having a molecular weight of at least 1        million Da), PB, and an aromatic polyazole from a spinneret        comprising extrusion holes of a first average diameter and of a        second average diameter, wherein the first and second average        diameters differ by a factor of at least 1.2.

In a seventh aspect, the invention provides a spinneret for making acut-resistant yarn, the spinneret comprising extrusion holes of a first,smaller average diameter and of a second, larger average diameter,wherein the first and second average diameters differ by a factor of atleast 1.2.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Brief Description of theDrawings

FIG. 1 is a schematic diagram of a process for making yarn of thepresent invention.

FIGS. 2A-D illustrate spinnerets with various capillary patterns inaccordance with the present invention.

FIG. 3 illustrates one embodiment of a spinneret pack.

FIG. 4 shows a spinneret according to the invention as used in theExample.

ABBREVIATIONS

UHMWPE: ultra-high molecular weight polyethylene

PB: polypyridobisimidazole, represented by the formula:

wherein N is a nitrogen atom, H is a hydrogen atom, and O is an oxgyenatom. The number of repeating units, n, is not critical. Preferably,each polymer chain has from 10 to 25,000 repeating units, n.

dpf: denier per filament

Da: Dalton, unit of molecular weight

Definitions

For purposes herein, the term “filament” is defined as a relativelyflexible, macroscopically homogeneous body having a high ratio of lengthto width across its cross-sectional area perpendicular to its length.The filament cross section can be any shape, but is typically circular.Herein, the term “fibre” is used interchangeably with the term“filament”.

The expressions “larger”, “smaller”, “largest”, “smallest” and “medium”in relation to a filament or plurality of filaments refers to theaverage diameter or linear density of the filament or plurality offilaments.

“Diameter” in reference to a filament is the diameter of the smallestcircle that can be drawn to circumscribe the entire cross-section of thefilament. In reference to a hole in a spinneret, it refers to thesmallest circle that can be drawn to circumscribe the hole.

“Denier” the weight in grams per 9,000 m length of filament or yarn.

“Tex” the weight in grams of one kilometre of filament or yarn.

“Decitex” one tenth of a Tex.

The expressions “capillary” and “extrusion hole” are usedinterchangeably to mean the holes through which polymer is extruded inthe formation of filaments.

Yarns

The yarns produced from the spinnerets of the invention, having mixedaverage diameter filaments, show increased cut- and abrasion-resistance,as compared to conventional yarns comprising filaments of a singleaverage diameter. It is believed that the mixed diameter arrangement hasexcellent cut- and abrasion-resistance for two main reasons:

-   -   (1) The arrangement of thin filaments with thick filaments        permits “rolling” of the filaments with respect to one another,        thus dissipating the attacking force;    -   (2) The arrangement of thin filaments with thick filaments        permits increased packing, thus increasing the density of the        yarn, providing more material to resist the attacking force.

The inventors have chosen to refer to these yarns as being made offilaments having different average diameters. The expression “averagediameter” can be replaced with the expression “linear density” for analternate definition of the yarns. It is equally possible to refer tothe yarns as being made up of filaments having different lineardensities. The yarns may be referred to as “mixed filament yarns”,“mixed denier yarns” and/or “mixed dtex yarns”.

For p-aramid (e.g., Kevlar®), average diameter of a filament can beconverted to linear density approximately as shown below:

Relationship between average diameter of filament and linear density forp-aramid Average diameter of filament Approximate equivalent linear(microns) density in denier per filament (dpf) 8 0.7 12 1.5 16 2.7

Polymer

The yarns made with the spinnerets of the present invention may be madewith filaments made from any polymer that produces a high-strengthfibre, including, for example, polyamides, polyolefins, polyazoles, andmixtures of these.

When the polymer is polyamide, aramid is preferred. By aramid is meant apolyamide wherein at least 85% of the amide (—CONH—) linkages areattached directly to two aromatic rings. Suitable aramid fibres aredescribed in Man-Made Fibres—Science and Technology, Volume 2, Sectiontitled Fibre-Forming Aromatic Polyamides, page 297, W. Black et al.,Interscience Publishers, 1968. Aramid fibres and their production are,also, disclosed in U.S. Pat. Nos. 4,172,938; 3,869,429; 3,819,587;3,673,143; 3,354,127; and 3,094,511.

The preferred aramid is a para-aramid. The preferred para-aramid ispoly(p-phenylene terephthalamide) which is called PPD-T. By PPD-T ismeant the homopolymer resulting from mole-for-mole polymerization ofp-phenylene diamine and terephthaloyl chloride and, also, copolymersresulting from incorporation of small amounts of other diamines with thep-phenylene diamine and of small amounts of other diacid chlorides withthe terephthaloyl chloride. As a general rule, other diamines and otherdiacid chlorides can be used in amounts up to as much as about 10 molepercent of the p-phenylene diamine or the terephthaloyl chloride, orperhaps slightly higher, provided only that the other diamines anddiacid chlorides have no reactive groups which interfere with thepolymerization reaction. PPD-T, also, means copolymers resulting fromincorporation of other aromatic diamines and other aromatic diacidchlorides such as, for example, 2,6-naphthaloyl chloride or chloro- ordichloroterephthaloyl chloride or 3,4′-diaminodiphenylether.

Additives can be used with the aramid and it has been found that up toas much as 10 percent or more, by weight, of other polymeric materialcan be blended with the aramid. Copolymers can be used having as much as10 percent or more of other diamine substituted for the diamine of thearamid or as much as 10 percent or more of other diacid chloridesubstituted for the diacid chloride or the aramid.

When the polymer is polyolefin, polyethylene or polypropylene arepreferred. By polyethylene is meant a predominantly linear polyethylenematerial of preferably more than one million molecular weight that maycontain minor amounts of chain branching or comonomers not exceeding 5modifying units per 100 main chain carbon atoms, and that may alsocontain admixed therewith not more than about 50 weight percent of oneor more polymeric additives such as alkene-1-polymers, in particular lowdensity polyethylene, propylene, and the like, or low molecular weightadditives such as anti-oxidants, lubricants, ultra-violet screeningagents, colorants and the like which are commonly incorporated. Such iscommonly known as extended chain polyethylene (ECPE) or ultra highmolecular weight polyethylene (UHMWPE). Preparation of polyethylenefibers is discussed in U.S. Pat. Nos. 4,478,083, 4,228,118, 4,276,348and Japanese Patents 60-047,922, 64-008,732. High molecular weightlinear polyolefin fibres are commercially available. Preparation ofpolyolefin fibres is discussed in U.S. Pat. No. 4,457,985.

When the polymer is polyazole, suitable polyazoles are polybenzazoles,polypyridazoles and polyoxadiaoles. Suitable polyazoles includehomopolymers and, also, copolymers. Additives can be used with thepolyazoles and up to as much as 10 percent, by weight, of otherpolymeric material can be blended with the polyazoles. Also copolymerscan be used having as much as 10 percent or more of other monomersubstituted for a monomer of the polyazoles. Suitable polyazolehomopolymers and copolymers can be made by known procedures, such asthose described in U.S. Pat. No. 4,533,693 (to Wolfe, et al., on Aug. 6,1985), U.S. Pat. No. 4,703,103 (to Wolfe, et al., on Oct. 27, 1987),U.S. Pat. No. 5,089,591 (to Gregory, et al., on Feb. 18, 1992), U.S.Pat. No. 4,772,678 (Sybert, et al., on Sep. 20, 1988), U.S. Pat. No.4,847,350 (to Harris, et al., on Aug. 11, 1992), and U.S. Pat. No.5,276,128 (to Rosenberg, et al., on Jan. 4, 1994).

Preferred polybenzazoles are polyzimidazoles, polybenxothiazoles, andpolybenzoxazoles. If the polybenzazole is a polyzimidazoles, preferablyit is poly[5,5′-bi-1H-benzimidazole]-2,2′-diyl-1,3-phenylene which iscalled PBI. If the polybenzazole is a polybenxothiazole, preferably itis a polybenxobisthiazole and more preferably it ispoly(benxo[1,2-d:4,5-d′]bisthiazole-2,6-diyl-1,4-phene which is calledPBT. If the polybenzazole is a polybenzoxazole, preferably it is apolybenzobisoxazole and more preferably it ispoly(benzo[1,2-d:4,5-d′]bisoxazole-2,6-diyl-1,4-phenylene which iscalled PBO.

Preferred polypyridazoles are rigid rod polypyridobisazoles includingpoly(pyridobisimidazole), poly(pyridobisthiazole), andpoly(pyridobisozazole). The preferred poly(pyridobisozazole) ispoly(1,4-(2,5-dihydroxy)phenylene-2,6-pyrido[2,3-d:5,6-d′]bisimidazolewhich is called PB. Suitable polypyridobisazoles can be made by knownprocedures, such as those described in U.S. Pat. No. 5,674,969.

Preferred polyoxadiaoles include polyoxadizaole homopolymers andcopolymers in which at least 50% on a molar basis of the chemical unitsbetween coupling functional groups are cyclic aromatic or heterocyclicaromatic ring units. A preferred polyoxadizaole is Oxalon®.

Method and Spinnerets

Although mixed dtex yarns can be made by “off-line assembly”, that is,the different denier filaments can be assembled after spinning, acontinuous filament yarn produced by direct spinning (i.e., using aspinneret having different size holes to produce directly a yarn havingmixed dtex filaments) is preferred. Off-line assembly is less preferredthan direct spinning since it can lead to segregation of the filamentsof different diameters, resulting in a non-homogeneous yarn which hasless resistance to attacking forces.

The continuous filament mixed diameter yarns are made using a spinnerethaving holes of different diameters. Holes of smaller diameter willyield lower diameter filaments, and holes of larger diameter will yieldlarger diameter filaments. The arrangement of the larger holes withrespect to the smaller holes in the spinneret is not of particularimportance, however, it is advantageous to have smaller diameterfilaments sandwiched between larger diameter filaments, as thismaximizes rolling action of the filaments. In a preferred arrangement,the arrangement of holes in the spinneret is in the form of concentriccircles, the whole forming a large circular array of holes. The holestoward the centre of the array are the smaller diameter holes, and thosetowards the circumference of the array are the larger diameter holes.Examples of different kinds of spinneret hole arrangements are shown inFIGS. 2A-E and 4. The arrangement shown in FIG. 4 has filaments arrangedin concentric order from the centre as follows: medium capillaries thensmall ones then medium again and finally large capillaries at theperiphery. This provides a very stable yarn in terms of segregation andstability during processing. The smaller filaments are “squeezed” in thetwo layers of larger ones. The pressure distribution in thisconfiguration is more favorable to spinning without dripping.

The cross-section of the filaments used in mixed dtex yarns may be, forexample, circular, elliptical, multi-lobed, “star-shaped” (refers to anirregular shape having a plurality of arms coming off a central body),and trapezoidal. The holes in the spinneret are chosen according to thedesired filament diameter and cross-section.

The “linear density” of the filament is determined by the rate(mass/time) at which polymer is extruded through a spinneret hole vs.the rate (speed, or linear distance/time) at which the filament isproduced. The size (diameter) of the filament is a function of thepolymer density and the fiber “linear density”. The number of holes in aspinneret (or section of a spinneret) is determined by the number offilaments desired in the final fiber bundle (“linear density” of whichis the sum of the individual filaments contained therein). The size andshape of each hole in the spinneret is influenced by the pressure-drop,shear, spin-stretch, and orientation needed to produce the desiredfilament diameter. In a preferred embodiment of the p-aramid spinneret,the smaller holes have a diameter of between at or about 35-65 microns,more preferably at or about 50 microns, and the larger holes have adiameter between at or about 60 to 90 microns, more preferably at orabout 64 microns. Preferably the ratio between the diameter of thelarger holes to that of the smaller holes is at or about 1.2 to at orabout 3, more preferably at or about 1.3 to 2.5. To make a yarn havingthree different diameter filaments, a spinneret may be used, forexample, in which the holes are in the following ranges: smallest 35 to65 microns (preferably 45-55 microns), medium 64-80 microns, largest 75to 90 microns.

The spinneret is made of material suited to the polymer or polymersolution or suspension that will be spun. For p-aramid spun fromconcentrated H₂SO₄, preferred material are tantalum, tantalum-tungstenalloys, and gold-platinum (rhodium) alloys. Other materials which may beused include high grade stainless steels [i.e., with a high chromium(>15 wt %) and/or nickel (>30 wt %) content], such as Hastelloy® C-276,ceramics and nanostructures made with ceramics. p-Aramid spinnerets mayalso be made from mixed materials, such as pure tantalum clad on atantalum-tungsten alloy. Materials other than tantalum can be used forthe cladding layer so long as they have the required corrosionresistance and annealed yield strengths of less than 30,000 psi (2,110kg/cm²). Among such suitable materials, listed in order of increasinghardness, are gold, M-metal (90% gold/10% rhodium by weight), C-metal(69.5% gold/30% platinum/0.5% rhodium by weight), D-metal (59.9%gold/40.0% platinum/0.1% rhenium by weight), and Z-metal (50.0%gold/49.0% platinum/1.0% rhodium by weight). The latter wassubstantially the same hardness as tantalum. Also suitable is a 75%gold/25% platinum alloy. All of these metals are, however, much moreexpensive than tantalum. All but Z-metal are much more easily damaged inuse than tantalum. Softer materials are advantageous, however, whencapillaries of quite high L/D ratio (e.g., greater than 3.5) are to beformed.

The polymer is extruded, either as a solution, suspension or melt,through the spinneret, and the resulting filaments are spun into yarnand treated in a manner suitable for the particular polymer.

A group of filaments may be classified as having the same averagediameter if the deviation of the average diameter of any filament in thegroup from the average is less than at or about 0.4 micron.

In a preferred embodiment, two sizes of filaments make up the yarn. Inthis case, it is preferred that the smaller filaments have an averagediameter in the range of at or about 8 to 22 microns, and the largerfilaments have an average diameter in the range of at or about 16 to 32microns. Although these ranges overlap, it is understood that thesmaller and larger filaments are chosen to have different averagediameters, such that the average diameter of the smaller filaments issmaller than the average diameter of the larger filaments. For example,included in the invention is a yarn having smaller filaments withaverage diameter of at or about 8 microns together with larger filamentshaving average diameter of at or about 16 microns, and a yarn havingsmaller filaments with average diameter of at or about 22 micronstogether with larger filaments having average diameter of at or about 32microns.

In yarns consisting of two sizes of filaments, it is preferred that thesmaller filaments not differ from the larger filaments by more than afactor of at or about 2, more preferably not more than a factor of at orabout 1.5. If the filaments differ too much in size, segregation canoccur, leading to nonhomogeneity and reduced cut-resistance. Preferablythe ratio of the diameter of the larger filaments to the smallerfilaments is at or about 1.3-1.5.

In those embodiments in which the yarn is made up of filaments havingtwo different average diameters, the second plurality of filaments(i.e., larger average diameter) make up from at or about 20 to 60% (bynumber) of the filaments in the yarn, and the first plurality offilaments (i.e., smaller diameter) make up from at or about 40 to 80%(by number) of the filaments in the yarn. More preferably the largerdiameter filaments make up from at or about 45 to 55% (by number) of thefilaments in the yarn, and the smaller diameter filaments make up fromat or about 45 to 55% (by number) of the filaments in the yarn.

In another preferred embodiment, three sizes of filaments make up theyarn. In this case, it is preferred that the smallest filaments have anaverage diameter in the range of at or about 4 to 10 microns (morepreferably at or about 6 to 9 microns), the medium filaments have anaverage diameter in the range of at or about 10 to 13 microns, and thelargest filaments have an average diameter in the range of at or about14 to 18 microns. For example, an advantageous result is obtained with ayarn made up of filaments having the following average diameters: 8, 12and 16 microns. In those yarns having three sizes of filaments,preferably the ratio of the average diameter of smallest:medium:largestis at or about 2:6:8, more preferably at or about 2:3:4.

In those embodiments in which the yarn is made up of filaments havingthree different average diameters (linear densities), the thirdplurality of filaments (i.e. the largest) make up at or about 15 to 35%(by number) of the filaments in the yarn, the second plurality offilaments (i.e., the medium) make up at or about 30 to 45% (by number)of the filaments in the yarn, and the first plurality of filaments(i.e., the smallest) make up from at or about 30 to 45% (by number) ofthe filaments in the yarn.

In other preferred embodiments, the yarn is made up of four, five, sixor more sizes of filaments.

In a further embodiment, referred to as “continuous”, the yarn consistsof a largest filament or group of filaments (e.g., average diameter ofat or about 15-40 microns) and a smallest filament or group of filaments(e.g. average diameter of at or about 4-25 microns) wherein the largestfilament (or group of filaments) and the smallest filament (or group offilaments) have different average diameters, and a plurality offilaments having average diameters distributed between the averagediameter of the largest filament and the smallest filament. With such anarrangement, very high packing densities (>90%) can be obtained,resulting in highly cut-resistant yarns.

The size of the holes in the spinneret influences the average diameterof the extruded filaments. The tension used to draw the filaments(drawing) also influences the average diameter of the filaments and thecharacteristics of the finished yarn. Drawing reduces the averagediameter of the filaments.

By adjusting the velocity of the fibre as it leaves the coagulating bathto higher than the velocity of the polymer as it emerges from thespinning holes one can adjust various physical properties of thefilament such as its tenacity, modulus and elongation, and also itsdiameter. The ratio of the two speeds here referred to, is calledspin-stretch in p-aramids in which the filament is set in thecoagulation batch and drawing ratio when referring to a fiber such asUHMWPE which is extended substantially after the fiber is quenched. Highdrawing ratio achievable with UHMWPE can reach up to 50-100 times. Withp-aramid a typical spin-stretch ratio is approximately 2 to 14.

The filaments making up the mixed dtex yarns may have a substantiallycircular cross-section. A circular cross-section maximizes the “rolling”of the filaments with respect to each other, thus maximizingcut-resistance. A circular cross-section also maximizes the packingdensity, also beneficial for cut-resistance. In alternative embodiments,the cross-section of the filaments may be elliptical. It is alsopossible for the smaller filaments to be circular in cross-section andthe large filaments to be elliptical in cross-section, or vice versa.The cross-section of the filaments is influenced by the shape of theholes in the spinneret, with round holes resulting in a circularcross-section, and elliptical holes resulting in an ellipticalcross-section. It is also influenced by the internal capillary shape,grooves and channels parallel or helicoidally arranged. Further, it isinfluenced by the coagulation process; for instance, m-aramid (e.g.,Nomex®) filaments typically have a two-lobe “dog-bone” shape when dryspun, or are multi-lobed, or “star shaped” when wet spun, since the skinis solidified before the solvent is extracted from the core, and thecontracted area does not “fill” the perimeter.

The yarn preferably has a tenacity of at or about 15 to 40 g/denier,more preferably at or about 25 to 35 g/denier.

The yarn of the invention preferably has an elongation at break of at orabout 1.5 to 15%, more preferably at or about 2 to 4%.

The yarn preferably has a modulus of elasticity of at or about 5 to 450N/tex, more preferably at or about 50 to 400 N/tex.

In a preferred embodiment, the yarn has a tenacity of at or about 25 to35 g/denier, an elongation at break of from at or about 2 to 4%, and amodulus of elasticity of from at or about 50 to 400 N/tex.

The number of filaments making up the yarn is not limited, and dependson the end-use, and the linear density required in the final yarn.Typical yarns comprise from 16 to 1500 total filaments. In a preferredembodiment, the total number of filaments in the yarn is 276, of which45-55% (in number) are the smaller filaments and 45-55% (in number) arethe larger filaments.

In yarns of the invention having a third plurality of filaments, withgreater average diameter than the first and second plurality offilaments, an example would be 276 total filaments in the yarn, with25-50% (by number) being the smallest filaments, 25-50% (by number)being the medium filaments and 15-35% (by number) being the largestfilaments.

The multi-dtex yarn made from the spinnerets of the invention preferablyhas a maximum possible packing density of at or about 80 to 95%, morepreferably at or about 90 to 95%. Cross section and packing density canbe measured by immobilizing the fibre under a relatively small tensionin an epoxy resin placed in a cylindrical mould perforated at the bottomto allow passage of the fibre flow of the resin. The molded sample isthen cured at room temperature for 12 hours. The sample is then frozenin liquid nitrogen for one minute and a cut transverse to the fibre axisis made to realize image analysis and diameter measurement and voidratio evaluation under SEM microscope enlargement. The samplepreparation used is well know for scanning microscopy except thatpolishing is avoided.

Packing density is influenced by the relative diameters (i.e., lineardensity) of the filaments, and the ratio of the number of firstplurality of filaments (i.e., smaller) to the number of the secondplurality of filaments (i.e., larger). Yarns having a ratio of firstplurality of filaments to second plurality of filaments of at or about0.5 (i.e., 50% by number smaller filaments and 50% by number largerfilaments), and a large difference in average diameter between thefilaments (large:small at or about 2) will typically have a high packingdensity (e.g. preferably greater than 90%, typically 90 to 95%). Inaddition, yarns made in the “continuous” embodiment also have highpacking densities.

With a filament mix comprising 57 filaments of 12 micron in the centre,115 filaments of 8 micron concentrically positioned around the firstlayer, then another 58 filaments of 12 micron concentrically positionedaround the second layer and 46 filaments of 16 micron externallypositioned around the third layer, one can obtained a packing density ofapproximately 90%.

The multi-dtex yarn is particularly suited to making cut-, abrasion- andpenetration-resistant fabrics, having excellent comfort characteristics.Such fabrics may be made by braiding, knitting or weaving techniquesknown in the art. Fabrics made from the yarns of the invention may beused for making cut-, abrasion- and penetration-resistant garments, forexample, gloves, footwear, coveralls, trousers and shirts, as well asparts of garments that require particular cut-, abrasion- andpenetration-resistance, such as the palms of gloves, cuffs of trousers,coveralls or shirts. Such articles may be coated with various resins andelastomers.

Additionally, multi-dtex yarns may be incorporated in unidirectionalprotective structures, in which largely unidirectional (parallel) yarnsare imbedded or partially imbedded in an immobilizing medium, such as aresin and elastomers.

EXAMPLES

Temperature: All temperatures are measured in degrees Celsius (° C).

Denier is determined according to ASTM D 1577 and is the linear densityof a fibre as expressed as weight in grams of 9000 meters of fibre. Thedenier can be measured on a Vibroscope from Textechno of Munich,Germany. Denier times (10/9) is equal to decitex (dtex).

Method for Making Yarn

Referring to FIG. 1, in a process described at (10), a yarn according tothe invention was made using as polymer a batch solution preparation ofpoly-para-phenylene terephthalamide containing 4.5 kg of polymer. 18.6kg of acid were pumped into a mixer and cooled to −22° C. while beingagitated to form a frozen slush in a nitrogen atmosphere (12). One-halfto one-third of the polymer was initially added and mixed for tenminutes before the remaining amount of polymer was added. The jacketsurrounding the mixer was then heated to 87° C. (14). Once the solutionhad maintained that temperature for an hour and a half, the mixeragitator and the vacuum pump were shut off, and the mixer waspressurized to 1.7 bar (absolute) with nitrogen.

After the polymer solution batch was made, a 5 cm³ meter pump (16) wasused to transfer the solution through a flow plate (22) and a screenpack (20), shown in FIG. 3 at (18), to the spinning process, whichoperated at 460 m/min. A 276 hole spinneret (24), shown in FIG. 4, wasused to spin the yarn. For the yarn of this example, the spinneret had46 holes with a 76μ capillary diameter (24 a), 115 holes with a 64μcapillary diameter (24 b), 115 holes with a 51μ capillary diameter (24c), and the hole arrangement is shown in FIG. 4.

Referring to FIG. 3, the filaments were spun through a 6 mm air gap (26)before entering a 3° C. quench bath (28) water and passing through aquench jet (30) (6.4 mm diameter radial jet with a 0.2 mm gap). The jetand tray flows for the quench bath were set to 2.3 l/min. and 5.3 l/min.respectively. Referring to FIG. 1, after the yarn was quenched, it wasconveyed to an acid wash of water (32). There were 30 wraps on a pair of113 mm diameter rolls (34) with a centreline spacing of 445 mm. Thewater flow was 15 l/min. and the tension was between 0.7 and 1.0g/denier (0.0.8 and 1.1 g/dtex). After the acid wash, the yarn moved onto a further wash cabinet (36) where there were also 30 wraps on a pairof rolls with the same diameter and centreline spacing as the acid washrolls. The first half of the wash cabinet was a caustic wash (38)(consisting of sodium hydroxide solution), and the second half was awater wash (40). The strong and dilute caustic flows for the causticwash were each 7.5 l/min., and the tension was between 0.5 and 0.8g/denier (0.55 and 0.89 g/dtex). The yarn was then dried at 311° C. with34 wraps on a pair of 160 mm diameter rolls (42) with a centrelinespacing of 257 mm. After the yarn was dried, a finish was applied (44)and it was wound on a packaging roll (46).

Inventive Sample

The inventive sample was made from a yarn of 400 denier out of aspinneret as depicted in FIG. 4, as follows:

-   -   46 capillaries yielding 2-2.6 dpf (about 16 micron in diameter)        filaments (24 a);    -   115 capillaries yielding 1.5 dpf (about 12 micron in diameter)        filaments (24 b); and    -   115 capillaries yielding 0.65-1 dpf (about 8 micron in diameter)        filaments (24 c).

The yarn was knitted to yield a sample of areal density of about 400g/m².

Control Sample

The control sample was made using yarn made exactly as specified above,but the spinneret had only one size hole and yielded only 1.5 dpf (about12 micron in diameter) filaments. The resulting yarn was 400 denier andconsisted exclusively of 1.5 dpf filaments. The yarn was knitted toyield a sample of areal density of about 400 g/m².

Testing of the Mixed dtex Yarns Cut Resistance Abrasive Cut Procedure

The abrasive cut testing procedure was based on the EN388:1994(Protective gloves against mechanical risks) current procedure, whichwas modified in terms of the weight force applied onto the circularblade, i.e., instead of a 5N equivalent force a 2.9N equivalent forcewas applied, thereby permitting an increased number of cut cycles, whichpromotes abrasion.

The procedure is described in the EN document. It can be summarized asfollows:

Two layers of a rectangular shaped sample (approx. 80 by 100 mm), one onthe top of the other, were tested simultaneously. A load of 2.9N insteadof 5N was positioned in its dedicated position. The test specimen sat ona support covered by a conductive rubber. The horizontal movement of thecircular rotating blade was 50 mm long. The resulting linear peripheralspeed was 10 cm/s. The cut tester was equipped with an automatedelectro-conductive system, which detected cuts throughout the specimen.

The blade sharpness was checked at the beginning and between each sampletesting using a cotton standard fabric as per specification ofEN388-1994 procedure.

Based on the number of cycles and a proposed calculation, provided inthe EN388-1994, a cut level was computed, whereby a cut level between 0to 5 was determined, 0 being the lowest achievable cut protection level,and 5 being the highest.

Results

The inventive sample required more than 300 cycles to cut through,whereas the control one made of 100% identical filaments required lessthan 150 cycles to cut through.

1. A spinneret for making a cut-resistant yarn, the spinneret comprising extrusion holes of a first, smaller average diameter and of a second, larger average diameter, wherein the first and second average diameters differ by a factor of at least 1.2.
 2. The spinneret of claim 1, comprising extrusion holes having two different average diameters, wherein the smaller extrusion holes have an average diameter of at or about 35-65 microns, the larger extrusion holes have an average diameter of at or about 60-90 microns.
 3. The spinneret of claim 1, comprising extrusion holes having three different average diameters, wherein the smallest extrusion holes have an average diameter of at or about 35-65 microns, the medium extrusion holes have an average diameter of at or about 64 to 80 microns, and the largest extrusion holes have an average diameter of at or about 75 to 90 microns.
 4. The spinneret of claim 1, comprising extrusion holes having two different average diameters, wherein the first plurality of extrusion holes represents at or about 40 to 80% by number of the extrusion holes in the spinneret.
 5. The spinneret of claim 1, comprising extrusion holes having three different average diameters, wherein the smallest extrusion holes make up at or about 30 to 45% by number of the extrusion holes in the spinneret, the medium filaments make up at or about 30 to 45% by number of the extrusion holes in the spinneret, and the largest extrusion holes make up at or about 15 to 35% by number of the extrusion holes in the spinneret.
 6. The spinneret of claim 1, comprising extrusion holes of two different average diameters, wherein the ratio of the average diameter of the larger extrusion holes to the average diameter of the smaller extrusion holes is between at or about 1.3-2.0.
 7. The spinneret of claim 1, comprising extrusion holes having a substantially circular shape.
 8. The spinneret of claim 1, comprising at or about 16% by number extrusion holes of at or about 76 micron diameter, at or about 42% by number extrusion holes of at or about 64 micron diameter, and at or about 42% by number extrusion holes of at or about 51 micron diameter.
 9. The spinneret of claim 1, comprising extrusion holes arranged concentrically, in which the smaller extrusion holes are arranged concentrically within the larger extrusion holes. 